Such rotary tools are used either to cut slots in solid materials or for cutting off portions of the materials by cutting through the material. The rotary tools comprise discs with centrally keyed mounting apertures and having peripherally disposed cutting elements. Originally the cutting elements were an integral part of the disc. When the cutting element wore out or broke the entire tool had to be replaced. To obviate the need for replacing the entire tool, recesses were cut in the periphery of the saw disc or saw blade to be used to receive replaceable teeth. Various methods and apparatus were used for properly attaching the teeth to the disc. An early patent showing a saw blade having a disc-like body with replaceable blades in peripheral recesses is French Pat. No. 88481 to M. Arnold which issued in January 1870.
It was later determined that in many cases, as the replaceable cutting insert broke when hitting an obstacle such as a harger material in the workpiece, the disc also was damaged. Thus, the problem remained of having to exchange the expensive disc if one or two of the replaceable inserts hit an obstacle and caused damage to the disc.
Thus, the problem remained of having to exchange the expensive disc if one or two of the replaceable inserts hit an obstacle and caused damage to the disc.
To overcome this problem the replaceable cutting insert was attached to a seat and larger recesses were cut into the periphery of the rotary disc for receiving the seat and an integral cutting insert. An example of this solution to the problem is shown in French Pat. No. 1,280,280 which issued to Lennartz and Co. in Nov. 28, 1960.
The replaceable seats for solving the problem of preventing a disc cracking or breaking is relatively new. However, seats on shanks have been used for receiving cutting inserts in saw blades since the 1870's. In the early patents the seats were used primarily as a means for locking the replaceable insert into the rotating disc.
An example of such use is a U.S. Pat. No. 151,043 which issued on May 19, 1874 to W. P. Miller. That patent teaches the use of a spring tempered steel seat arrangement for holding cutting inserts into recesses in the periphery of a rotating saw. A shank-like seat is slightly larger than the recess in the disc and is of tempered steel so that when the seat is forced into a recess it compresses and secures the cutting insert in place. The shank-like seat of the Miller device only extends into the recess until the shoulder of the shank-like seat abuts a shoulder abutting portion of the outer periphery of the disc.
In the Miller device there are combinations of forces acting on the shoulder abutting portion. For example, there are the counter forces to the compression forces of the resilient shank that act on the shoulder abutting portion. In addition the cutting forces act on the shoulder abutting portion. The combination of forces can damage the disc. Thus, in spite of the replaceable shank-like seat and insert there still remains a great likelihood of damage to the disc itself.
Other prior art devices for holding replaceable blades in place are shown in patents such as U.S. Pat. No. 207,121 which issued to Van Drake on Nov. 7, 1882. In that patent the replaceable disc or cutting insert is held in place in a recess on the periphery of the saw disc by a resilient arcuate shim member. In Van Drake arrangement there are tremendous forces on the periphery of the disc including the cutting forces and the reactive resilient forces.
In a U.S. Pat. No. 320,798 to Smith which issued on Sept. 22, 1885, resilient replaceable cutting inserts are held in place using a seat in a peripheral recess plus a resilient shim. An embodiment taught in the Smith patent merely uses resilient cutting inserts. The necessary resiliency of the cutting insert makes it impossible to use materials such as carbide.
The U.S. Pat. No. 455,169 to Chase, which issued on Jan. 30, 1891, shows a replaceable insert held against the body by a unique block or holder consisting of a semi-circular segmental piece designed to turn into an arcuate groove in the recess for receiving the replaceable cutting insert. Note that the "holder" is not really a "seat" and thus the problems of needing to replace the entire disc if the seat fractures, remains.
The U.S. Pat. No. 542,577 to Walter which issued on July 9, 1895 shows an arcuate holder for holding a replaceable cutting insert or saw tooth within the body of the disc or saw. Therein the disc body takes the strains exerted on the tooth plus the reactive resilient strains and there is no seat protection.
The known prior art teaches replaceable cutting inserts with varied apparatus and systems for securely holding the replaceable cutting inserts in the saw body or disc. All of the known prior art teaches either integral seats and cutting edges or seating systems where the clamping forces for holding the cutting insert on the seat depends on the clamping of the seat in the body.